This invention relates to a data reproduction apparatus for reproducing character data from a character multiplexing video signal which is demodulated from a received signal of character multiplexing television broadcast, and more particularly to an apparatus for generating a clock signal for character data reproduction based on a character data identification sync signal attached to a character multiplexing video signal and reproducing character data based on the clock signal, and the apparatus is used for a television receiver or video tape player, for example.
The character multiplexing video signal contains character information in the form of character data or font data in the vertical scanning period of the video signal, and in a period prior to the character data, a bit sync signal called a CRI (Clock Run In) signal and a byte sync signal called an FC (framing code) signal are sequentially attached as the character data identification sync signal.
In the specification of the character multiplexing video signal, the CRI signal is 16 pulse signals (pulse signals of 8 cycles) having a pattern of "1010101010101010" and the FC signal is 8 pulse signals having a pattern of "11100100". The pulse period (frequency) of the CRI signal is determined according to the type of the specification.
Conventionally, in a data reproduction apparatus for character multiplexing video signal, the CRI signal in the character multiplexing video signal is detected to generate a clock signal for character data reproduction and the character data is reproduced based on the clock signal.
However, the CRI signal which conforms with the specification is not always contained in a video signal input of a video signal input terminal 10 even at the time of reception of the character multiplexing television broadcast according to the conditions of countries or regions giving the character multiplexing television broadcast and, for example, the period of the CRI signal is short or part of the pulse of the CRI signal is lost in some cases.
In such a case, in the conventional data reproducing apparatus, the CRI signal cannot be stably detected and a clock signal for character data reproduction cannot be stably generated, and as a result, character data cannot be stably reproduced in some cases.
Therefore, for example, when an equipment containing a data reproduction apparatus for character multiplexing video signal for export specification is manufactured, it is necessary to recheck whether a system for generating a clock signal for character data reproduction based on the CRI signal can be used or not.
As described above, the data reproduction apparatus for character multiplexing video signal has a problem that a clock signal for character data reproduction cannot be stably generated in some cases according to the conditions of the countries or regions giving the character multiplexing television broadcast, and therefore, character data cannot be stably reproduced in some cases.